1. Field of the Invention
The present invention relates to a flight management systems for aircraft, and more particularly to determining performance characteristics of the aircraft for use by the flight management system.
2. Description of the Related Art
A flight management system (FMS) is a fundamental component of the avionics on an aircraft. The FMS is a dedicated computer system that automates a wide variety of in-flight tasks, thereby reducing the workload on the flight crew. A primary function is in-flight management of the aircraft flight plan.
A navigation database, stored in the FMS, contains data for constructing the flight plan. This data includes information regarding airways and waypoints, holding patterns, airports, runways, and standard instrument departure paths. Information also is provided about radio navigation aids, including distance measuring equipment, VHF omnidirectional range systems, and non-directional beacons.
The flight plan is usually determined on the ground before departure, either by the pilot of smaller aircraft or an airline dispatcher. The flight plan then is entered into the FMS either via a cockpit keyboard, selection from a stored library of common routes, or via a datalink with the airline dispatch center. The flight plan includes the route, altitude and airspeed for each leg or segment of the trip. During preflight, other information relevant to managing the flight plan, such as gross weight of the aircraft, and fuel weight, is entered into the FMS.
During flight, the FMS constantly examines various on-board sensors to determine the aircraft's positional and performance parameters. From those parameters and the stored flight plan, the FMS calculates the course to follow. The pilot can follow this course manually or the autopilot can be set to follow the course. The flight plan in the FMS often is modified during the flight by the pilot. In which case, the FMS has to rebuild flight plan information.
There is a desire as part of the flight management process for the FMS to compute three dimensional trajectories of the aircraft operating under a set of profiles such as airspeed targets, engine thrust settings, speed and altitude constraints, forecasted winds, and other operational parameters in the climb, cruise, and descent phases of flight. Algorithms for that computation typically require knowledge of the engine fuel flow rate and the aircraft climb capability, which are characteristics specific to the particular airframe and engine combination. The necessary detailed aerodynamic models of the airframe and the engine for a specific aircraft, however, are only available from the aircraft manufacturer, which often considers that information highly proprietary. Thus the requisite aircraft performance data is usually unavailable to other companies that produce avionic equipment.
It is theoretically possible for an avionics manufacturer to measure operating characteristics of a given type of aircraft and use that data to build a multi-dimensional database from which to subsequently retrieve the desired fuel flow and climb rate parameters. Nevertheless, in order for these databases to be comprehensive enough for practical use in constructing aircraft trajectories during the flight plan process, such a large amount of empirical data would have to be gathered over a very great amount of flight time that such approach is not very practical. In addition, searching that large database to find the data providing the best match to a given set of operating conditions in the future requires a very exhaustive process. Thus such a database search presents such a significant obstacle as to render this approach impractical.
Even if this empiricalapproach was to be used, the particular database only could be used effectively with that one type of aircraft.
Therefore, it is desirable to develop another approach that requires a lesser amount of aircraft performance data to be able to derive reliable values for aircraft operating parameters, such as the engine fuel flow rate and the aircraft climb rate.